Apple Filling: Place the slices of apple in a large bowl and toss with the lemon juice. Add the sugars, ground cinnamon, nutmeg, and salt and toss to combine. Put the apples in a large strainer, cover with plastic wrap, and place over a large bowl (to capture the juices). Let the apples drain for about 1 to 2 hours.

While the apples are macerating, make the pie crust.

Pie Crust: In a food processor, place the flour, salt, and sugar and process until combined. Add the butter and process until the mixture resembles coarse meal (about 10 seconds). Add about 1/4 cup (60 ml) water and process until the pastry just holds together when pinched. If necessary, add more water. 

Turn the dough onto your work surface and gather into a ball. Divide the dough in half (about 335 grams each), flattening each half into a round, cover with plastic wrap, and refrigerate for about one hour or until firm. (This will chill the butter and relax the gluten in the flour.)

After the dough has chilled sufficiently, remove one portion of the dough from the fridge and place it on a lightly floured surface. Roll the pastry into a 12 inch (30 cm) circle. (To prevent the pastry from sticking to the counter and to ensure uniform thickness, keep lifting up and turning the pastry a quarter turn as you roll (always roll from the center of the pastry outwards).) Fold the dough in half and gently transfer to a 9 inch (23 cm) pie pan. Brush off any excess flour and trim the edges of the pastry to fit the pie pan. Cover with plastic wrap and place in the refrigerator. 

Then remove the second round of pastry and roll it into a 12 inch (30 cm) circle. Transfer to a parchment lined baking sheet, cover with plastic wrap, and place in the refrigerator. 

Apple Filling: After the slices of apples have macerated for about 1 to 2 hours, you should have about 1/2 cup (120 ml) of apple juice. Pour the juice into a saucepan. Place over medium high heat and boil the juices for about one minute. Then remove from heat. In a small bowl whisk the cornstarch with about 1/2 - 1 tablespoon water, until you have a thick paste. Whisk the cornstarch mixture into the apple juices. Return to heat and boil, whisking constantly, until the mixture is translucent (about 1-2 minutes). Let cool to room temperature.

Next, transfer the drained apples slices to a large bowl, add the cooled apple mixture, and toss to combine. Pour the apple filling into the chilled pie crust. Dot with the butter. Gently place the top crust over the apples. Tuck any excess pastry under the bottom crust and then crimp the edges using your fingers or a fork. Using a sharp knife, make five- 2-inch (5 cm) slits from the center of the pie out towards the edge of the pie to allow the steam to escape. Cover the pie with plastic wrap and place in the refrigerator to chill the unbaked pie while you preheat the oven.

Preheat the oven to 425 degrees F (220 degrees C). Place the oven rack in the lower third of the oven and place a baking sheet on the rack before preheating the oven.

In a small bowl whisk the egg with the water. With a pastry brush, brush the top of the chilled pie with the egg wash and sprinkle with granulated white sugar or sparkling sugar. Set the pie on the baking sheet and bake for about 45 to 55 minutes or until the pastry is golden brown and the juices start to bubble through the slits. If needed, cover the edges of the pie with a pie shield or foil to prevent over browning after about 30 minutes. Remove the pie from the oven and place on a wire rack to cool for about 3-4 hours before cutting. Serve warm or at room temperature with vanilla ice cream or softly whipped cream. Store at room temperature for 2 days or in the refrigerator for 3 to 4 days.

Makes one 9 inch (23 cm) pie.